Energy harvesting for vehicles

Energy harvesting comes to the fore with electric vehicles because the price they pay for being environmental and exhibiting many performance advantages is that they have limited energy available. In and on these vehicles, the energy snatched from heat, light, movement and other sources may be milliwatts or less to drive wireless sensors and actuators, watts for self sufficient lighting clusters (still in development) or - the main focus - up to kilowatts to charge the traction battery or traction supercapacitor that provide motive energy to the electric traction motors.

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ndarily, the traction power storage may also provide other electricity needs such as hard wired lights, climate control and instruments. Reducing any of these loads is welcome. The traction battery of an on-road electric vehicle can be up to half of the total cost of the vehicle - another sensitive issue. If the battery is charged more often in various ways it can often be smaller and cheaper and weigh less - a virtuous circle. IDTechEx examines the use of energy harvesting to charge traction batteries in the new report Energy Harvesting for Electric Vehicles 2011-2021 .

In the past, there has been some contempt for the usually small amount of electricity that energy harvesting can provide for traction. For example the old idea of a small square photovoltaic panel on an electric car may increase range by only five kilometers. This misses four points
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1. With the typical pure electric car or aircraft typically managing only 160 kilometers range, something totally unacceptable to most prospective purchasers, a few extra kilometers here and there actually add up to something meaningful in the marketplace. With autonomous unmanned vehicles (AUVs) having up to two forms of energy harvesting and superyachts having three, the day when EVs have at least five forms of energy harvesting is approaching.

2. Replacing wired devices such as sensors and actuators with wireless ones using energy harvesting increases the range of the vehicle by eliminating a considerable weight of wiring not just by providing independent electricity. Modern vehicles have a large and increasing number of sensors and actuators.

3. Existing forms of energy harvesting are improving rapidly. For example, thin, flexible photovoltaics is now available that can be wrapped around both the outside and inside of an electric vehicle and new forms harvest infrared as well as light with UV harvesting and transparency coming along later - the film will even go over windows and lights.

4. Other forms of energy harvesting generate huge amounts of energy, notably regenerative braking and energy harvesting shock absorbers (dampers) and active suspension. For example, an energy harvesting shock absorber on a truck can generate one kilowatt.
The following figure shows examples of energy harvesting technologies and their applicability to electric vehicles, land, water and air.
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Source: IDTechEx Energy Harvesting for Electric Vehicles 2011-2021 .

Energy harvesting is now receiving a great deal of attention because such devices can have life of twenty years or more and provide environmental, safety, security of supply and other benefits including cost.
Opportunities for energy harvesting in cars
The opportunities in cars include energy harvesting where motive power, not just accessories, benefit from locally harvested energy. Either way, the ambient energy available includes human power, vibration, light, heat and movement. The conversion mechanism can be photovoltaics (solar cells), thermovoltaics (Seebeck effect), piezoelectric (as with a batteryless gas lighter), electrodynamic (like a bicycle dynamo for example) or other options. Sometimes energy storage is needed with energy harvesting, in order to deliver the electricity that has been created at the right time and in the right amount for the application. This usually means rechargeable batteries and/ or supercapacitors/ combinations of the two into one device, which is being explored and these devices are variously called supercabatteries, bacitors or Asymmetric Double Layer Capacitors (ADLCs).

The most popular types of energy harvesting for all applications are photovoltaic and electromagnetic and this is also true with cars. Piezoelectric and thermoelectric options are being developed by hundreds of organisations and they will have many uses. These two options are starting to be used in cars but there is much more to come.
Market size of EV energy harvesting 2011-2021
Let us focus on the main segment which is providing electricity to the traction battery rather than to distributed small devices in the vehicle. Even here, one can only value the EV energy harvesting market for devices that do no other function. That leaves out energy harvesting shock absorbers (dampers), because they primarily act as shock absorbers, and regenerative braking which is simply a traction motor that works in reverse. The same is true of the marine and air versions of regenerative braking such as propellers working in reverse when under sail or soaring.

Here we ignore the energy harvesting used in small devices distributed throughout the vehicle and concentrate on on-board energy harvesting that feeds the traction battery with electricity. A possible scenario is shown below.

Possible scenario for number of EVs sold and the percentage using energy harvesting to charge traction batteries by type in 2011 and 2021, in numbers K
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